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Synthesis of rac-42. Reagents and conditions: a) MCPBA, CH2Cl2, 0 °C to rt, 45 min; b) TFA, H2O, THF, 60 °C overnight, c) acetone, PTSA, 3 h, rt; d) NaOMe, MeOH, 48 h, rt, 43% over 5 steps; e) (COCl)2, DMSO, Et3N, CH2Cl2, −78 °C to rt, 2 h; f) diethyl allylphosphonate, BuLi, THF, 0 °C to rt, overnight, 30% over 2 steps; g) 60% AcOH, 60 °C, 3 h, 63%. MCPBA = m-chloroperbenzoic acid, TFA = trifluoacetic acid, PTSA = p-toluenesulfonic acid.
